This invention relates to ultrasonic welding inspection methods and particularly to in-process nondestructive ultrasonic welding inspection methods.
There are many methods known in the art for ultrasonically inspecting welded members. Some of these methods are used during the welding process to inspect the welded joint. For example, an ultrasonic transmitter may be positioned on one electrode and an ultrasonic receiver positioned on another electrode, with the members to be welded positioned between the electrodes. In this method, the ultrasonic wave is transmitted from the ultrasonic transmitter through the weld to the ultrasonic receiver for inspecting the welded joint.
In another type of ultrasonic weld inspection, one ultrasonic transducer can function as both the transmitter and receiver for reflecting ultrasonic waves through the weld joint for inspection.
In U.S. Pat. No. 4,099,045 to Okuda et al. there is described an ultrasonic method for resistance welding. In the Okuda et al. method, an ultrasonic vibrator disposed on one of two opposed electrodes having two metallic plates sandwiched between them for being welded intermittently delivers a pulse-shaped ultrasonic wave to a reflecting surface located in the other electrode and receives the wave reflected from the reflecting surface. The vibrator converts the received wave to an electrical signal that is applied to a minimum sensor and a peak sensor, the minimum sensor senses and holds the minimum peak magnitude of the signal which is then subtracted from the peak magnitude of a similar signal developed within the peak sensor at the time of termination of the welding current. The resulting difference between the two magnitudes determines the weld condition of the welded plates.
Although many of the methods known in the art for ultrasonically inspecting a weld have provisions for inspecting during the welding process, those methods generally involve detecting a weld defect during the welding process and taking corrective action to eliminate the defect after the weld metal has solidified. Typically, the corrective action may be to reject the welded members or to reweld the defective area. Of course, this type of corrective action is expensive in both time and materials and may, nevertheless, result in a less than satisfactory weld due to problems related to reheating of the base metal.
Consequently, while there are many methods known in the art for ultrasonically inspecting a welded portion of a joint during the welding process, none of those methods inspects the molten weld before solidification for determining corrective action to eliminate weld defects before the weld joint has solidified.
Therefore, what is needed is an ultrasonic weld inspection method that inspects the molten weld, inprocess, for determining if the molten weld contains a defect and then taking corrective action to eliminate the weld defect before the weld joint solidifies.